The STEM is being used for mass measurement and the possible localization of specific groups by Au-labeling (carbohydrate or SH groups) in the study of the molluscan hemocyanins (Fic). The simplest of these decameric cylindrical macromolecules is ten times the size of the arthropodan hexameric Hc. The Hcs of marine gastropods consist of multiple decameric cylinders assembled into di-decamers, and of particular interest, tri-decamers and higher arrays. Several different methods of purif~ring the hemocyanin from P. gigantea were examined in the STEM for their quality. The hope is to be able to perform SAS experiments on them, similar to those described for ClpP (see Flanagan) Many other hemocyanins have been compared to try to discover what determines the preferred number of decamers for a particular organism. Carbonic anhydrase is the enzyme used by oyster in shell formation. This has been purified and shown to be composed of 35kD subunits. Unlike the vertebrate complex which flinctions as a 30kl) monomer, the snail enzyme is a complex of roughly 2MD. STEM mass measurements are being used to determine the number and spatial arrangement of subunits.